The present invention relates to a technical field of plasma processing such as a film formation by plasma CVD, in particular, to a plasma apparatus and a plasma processing method making it possible to perform a continuous processing on an elongated substrate by an ICP system allowing a high quality and high speed processing.
As plasma forming methods for a plasma CVD apparatus, there are known a capacitively coupled plasma (CCP) system and an inductively coupled plasma (ICP) system.
In the CCP plasma system (hereinafter referred to as CCP system), a high frequency voltage is applied to two electrodes opposed to each other, thereby forming plasma between the electrodes.
The CCP system is advantageous, for example, in that it is of a simple construction and that it can easily meet a demand for an increase in size through an increase in the electrode area. Further, it is also advantageous in that, by forming a large number of through-holes in the electrodes and supplying gases (plasma gas and reaction gas) like a shower therethrough, it is possible to uniformly supply the gases to the entire film formation region (the gases can be easily made uniform) even if the areas of the electrodes are increased.
Thus, the CCP system is most widely used for plasma CVD in, for example, the field of production of semiconductor devices and liquid crystal devices.
On the other hand, the CCP system has a problem in that the electron density of the plasma is rather low (approximately 1×108 to 1×1010 cm−3) and that it is rather difficult to achieve an improvement in terms of film formation speed. Further, since the electrodes exist in the region where the plasma is formed, a film is also accumulated on the electrodes if the film formation is continued for a long period of time, making it impossible to perform a proper film formation.
As disclosed in JP 2005-219427 A and the like, for mass production, there is known a method according to which an elongated substrate is fed out of a roll formed by winding a substrate and in which a film formation by plasma CVD is effected by the CCP system while conveying the substrate which is wrapped around a drum. Here, in the CCP system, in order to form a high quality film, it is necessary to maintain the distance between the two electrodes with a high precision on the order of several hundred to several thousand μm. When such a drum is used in the CCP system, the drum constitutes one electrode; in this case, however, it is necessary to form the surface of the opposing electrode as a curved surface with a high precision in conformity with the drum and to arrange the electrodes with high positional accuracy, making it rather difficult to design the electrodes.
Further, in the CCP system, the requisite pressure for maintaining the plasma is rather high (which is usually approximately several tens to several hundred Pa), so in the case in which, as disclosed in JP 2005-219427 A and the like, a plurality of film formation spaces (film formation chambers) are connected together to continuously perform the film formation, mixing-up of gases may occur between the film formation chambers, resulting in a deterioration in film quality, etc.
As disclosed in JP 06-76281 A and JP 2000-96239 A, in the ICP plasma system (hereinafter referred to as ICP system), a high frequency power is supplied to an (induction) coil to thereby form an induction magnetic field to form an induction electric field, by means of which plasma is generated.
In the ICP system, in which a high frequency power is supplied to a coil to thereby form an induction electric field to generate plasma, there is no need to provide an opposing electrode, further, it is possible to easily generate plasma of a high density (1×1011 cm−3 or more). Further, plasma can be generated at low pressure and low temperature, making it possible to form a thin film of a satisfactory film quality. Further, when, as disclosed in JP 2005-219427 A, an elongated substrate is conveyed while wrapped around a drum, there is no need for the drum to serve as an opposing electrode, so the drum is electrically independent. Thus, it is possible to perform various controls independent of the electric field forming means, such as an application of bias potential using the drum.
In the ICP system, however, it is difficult to achieve an increase in size, so it is rather difficult to apply the system to a film forming apparatus of a large area or to a film forming apparatus as disclosed in JP 2005-219427 A in which the film formation by plasma CVD is continuously effected on an elongated substrate.